Apparatus and method for blending and dispensing foamable, curable organosiloxane compositions

ABSTRACT

An apparatus for preparing foams exhibiting a uniformly small cell size, a minimum number of ruptured cell walls and a smooth surface from foamable curable compositions comprises means to transport the ingredients of a foamable, curable composition to the input of a static mixer in which the ingredients of the composition are blended to homogeneity prior to being extruded into an exit zone and through an exit orifice. The length to diameter ratio of the mixing zone and the diameter of the exit orifice are within specified ranges.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a mixing and dispensing apparatus for foamablecompositions. More particularly, this invention relates to an apparatusand a method for blending and dispensing the ingredients of foamable,curable organosiloxane compositions. The cured foam is soft, flexibleand exhibits a uniform distribution of small diameter cells. The presentapparatus and method are particularly useful for preparing smalldiameter elongated articles such as foamed-in-place gaskets.

2. Background Information

Foamable organosiloxane compositions that generate hydrogen gas as ablowing agent during curing of the composition are known in the art, andare described in U.S. Pat. Nos. 3,923,705; 4,599,367; 4,888,217; and5,079,292.

The prior art also describes numerous devices for blending two-partcompositions containing a thermosetting organic or organosiliconepolymer with a compressed gas or a chemical blowing agent in a confinedarea and dispensing the resultant mixture into the atmosphere where theentrapped gas forms a foam as the composition cures. Devices of thistype are described in U.S. Pat. Nos. 4,778,631, which issued to Cobbs etal. and 5,082,142, which issued to Saidman et al. on Jan. 21, 1992. TheSaidman et al. patent teaches dissolving the blowing agent in the one ofthe two parts of the composition and blending the two parts in a staticmixer immediately prior to dispensing the composition from theapparatus.

The Saidman et al. patent does not require a particular nozzleconfiguration at the output of the static mixer to produce a usefulfoam.

An article by C. Rauwendaal entitled "A Guide To Static Mixers"(Plastics World, May 1992, pages 63-66) defines static mixers as devicesdesigned to "split and reorient the flow and, thus, impart improveddistributive mixing to the fluid". This article recommends mixers with alength to diameter ratio of at least 10 to achieve adequate mixing andproduct uniformity using the most efficient static mixers described inthe article. This mixers are identified as type SMX manufactured bySulzer and type ISG manufactured by Ross.

Rauwendaal considers static mixers containing the Kenics type of mixingelement simple and easy to clean, but less efficient. Mixers containingthese elements require a length to diameter ratio of at least 29 toachieve efficient mixing.

The present inventor discovered that when a static mixer is used, thediameter of the orifice through which the composition passes whenexiting the device is critical to preparing a foam exhibiting uniformcells that are preferably no larger than two millimeters and contain alow percentage, typically less than 10 percent, of cells with rupturedwalls. The present method and associated apparatus are based on thisdiscovery. In accordance with the present invention, nozzles with anexit orifice smaller than 1.50 mm permit use of a static mixercontaining Kenics type elements with a lower length to diameter ratio(11) than taught by the art, including the aforementioned article by C.Rauwendaal, which recommends a length to diameter ratio of at least 29to achieve product uniformity using this type of mixing element.

SUMMARY OF THE INVENTION

The ingredients of foamable organosiloxane compositions are blended anddispensed in a pressurized apparatus comprising a static mixer and anozzle with an exit orifice that does not exceed 1.50 mm in diameter.The resultant foams exhibit a uniformly small cell size, at most about 5percent of ruptured cell walls and a smooth surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an apparatus of the present inventionsuitable for use in dispensing two part organosiloxane compositions.

FIG. 2 is a diagrammatic view of the apparatus of FIG. 1 modified fordispensing one-part compositions containing a microencapsulatedcatalyst.

FIGS. 3, 4, 5 and 6 are cross-sectional views of four preferred exitzone and nozzle configurations.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides an apparatus for blending and dispensing afoamable organosiloxane composition, said apparatus comprising 1) amixing zone consisting essentially of a channel having an inlet and anoutlet and containing a plurality of static mixing elements positionedwithin the channel, where the ratio of the length of said channel to itsdiameter is at least 11, and 2) an exit zone communicating with theoutlet of said channel and comprising a nozzle containing an exitorifice where the diameter of said exit orifice does not exceed 1.50 mm.

This invention also provides a method for blending and dispensing afoamable organosiloxane composition, the method comprising transportingsaid composition under pressure first through a mixing zone consistingessentially of a channel having an inlet and an outlet and containing aplurality of static mixing elements positioned within the channel, wherethe ratio of the length of said channel to its diameter is at least 11,and second through an exit zone communicating with the outlet of saidchannel and comprising a nozzle containing an exit orifice where thediameter of said exit orifice does not exceed 1.50 mm.

The arrangement and interconnection of the components that constitutethe present blending and dispensing apparatus can be understood byreferring to FIG. 1 of the accompanying drawings. The two parts of afoamable organosiloxane composition are transported from theirrespective storage containers 10 and 11 through the apparatus by meansof a pump 12. The two parts of the composition enter a flow controlmanifold 13 through individual conduits 14 and 15 equipped with valves16 and 17 that control the flow of material through the conduits. Therelative flow rates in the two conduits is controlled using a meteringmanifold 18 equipped with a pressure gauge 19. The flow control andmetering manifolds constitute the entrance zone of the apparatus.

The two steams of ingredients of the foamable composition from themetering manifold are combined in the entrance section of a static mixer20 having a length to diameter ratio of at least 11:1.

Static mixers are well known in the art. This mixers are designed toprovide an efficient blending of ingredients flowing in a channelwithout use of moving parts. This is achieved by placing a plurality ofdevices or elements within the channel that split and reorient the flowof material within the channel. The elements are typically stacked in aseries with each element rotated 90 degrees with respect to the nextelement in the series. The configuration of these devices determines theefficiency of the mixer, which can be expressed as the minimum length todiameter ratio required to achieve a homogeneous blend of ingredientsexhibiting less than a 1% variation in composition between randomlyselected portions of the blended material.

The length to diameter ratio of static mixers used in accordance withthe present method is greater than 11.

The efficiency of static mixers containing various elementconfigurations is discussed in the article by Rauwendaal mentioned in apreceding section of this specification.

A preferred element configuration, based on its availability, simplicityand ease of cleaning is referred to as "Kenics". This element is in theform of a twisted tape. Other available elements are in the form ofbars, corrugated plates, and bent and split tapes. The length todiameter ratio of static mixers containing the Kenics type of mixingelement is preferably from 11 to 35.

During passage through the mixer the ingredients of the composition areblended to homogeneity before entering the exit zone 21 containing theexit orifice 22. The diameter of the exit orifice is critical to thecell structure of the final foam, and should be less than 1.50 mm.

An orifice diameter of below about 0.5 mm. will restrict the flow of thefoamable composition to the extent that the pressure used to transportthe composition through the present apparatus must be increased beyondconventional values to achieve a useful flow rate without any benefit inincreased quality of the cured foam. The diameter of the exit orifice ispreferably from 0.7 to 1.5 mm.

The apparatus shown in FIG. 2 is suitable for dispensing one-partfoamable organosiloxane compositions containing a catalyst that ismicroencapsulated in a layer of a thermoplastic resin. Storagecontainers 10 and 11 are replaced by a single container 10 and conduits14 and 15 by a single conduit. Because only one stream of ingredients ispresent, a metering manifold is no longer necessary.

The apparatus includes a heating device 28 that can be located betweenthe flow control manifold and the static mixer 20. The purpose of theheating device is to soften the resin encapsulating the catalyst,thereby allowing the catalyst to combine with the other ingredients ofthe organosiloxane composition. The catalyst is uniformly dispersedthroughout the composition in the static mixer.

Cross-sectional views of preferred exit zone configurations are depictedin FIGS. 3, 4, 5 and 6. The interior of the nozzle shown FIG. 3 iscylindrical in contour with a diameter from about 0.5 to about 1.5 cm.The exit orifice 22 is located on a surface 23 of a wall that issubstantially perpendicular with respect to the axis of the cylindricalexit zone and preferably from 2.5 to 12.7 mm thick.

The configuration shown in FIG. 4 contains the exit orifice at the apexof a conical section 24 that is adjacent to a cylindrical section 25.The interior angle defined by the inner surface of the conical sectionand the adjoining inner surface of the cylindrical section is from 135to about 160°

The configuration of FIG. 4 adds a needle-shaped flow control valve 26to the exit zone of FIG. 3. In a preferred embodiment the valve isbiased toward a position blocking exit orifice 22 by means of a spring(not shown). When it is desired to discharge material through the exitorifice, the valve is moved away from the orifice by applying sufficientpressure to offset the force exerted by the spring.

The configuration shown in FIG. 6 contains a passage 27 connecting theapex of the conical section 24 of the exit zone shown in FIG. 3 with theexit orifice 22. The diameter of this passage is substantially equal tothe diameter of the exit orifice and the passage can be from about 2.5to about 12.7 mm. in length.

THE FOAMABLE ORGANOSILOXANE COMPOSITION

Any of the known one and two-part curable organosiloxane compositionsthat generate a gas such as hydrogen as a by-product of the curingreaction can be used in the present mixing and dispensing apparatus.Preferred compositions of this type are described in U.S. Pat. Nos.4,599,367; 3,923,705; 4,888,217 and 5,079,292. Foamable compositions ofthis type contain an organohydrogensiloxane and at least one curablepolyorganosiloxane containing silicon-bonded hydroxyl groups and/orsilicon-bonded alkenyl radicals such as vinyl, allyl or hexenyl. If thecomposition does not contain a polyorganosiloxane with silicon-bondedhydroxyl groups, also referred to herein as silanol groups, the curablecomposition contains sufficient water and/or liquid alcohol to reactwith the organohydrogensiloxane to generate the hydrogen gas thatfunctions as the blowing agent during curing of the composition.

The curing and hydrogen generating reactions are catalyzed by a platinumgroup metal or a compound of such a metal. The term "platinum groupmetal" typically includes platinum, rhodium and palladium. The reactionbetween silanol groups and silicon bonded hydrogen atoms can becatalyzed by inorganic and organic tin compounds.

The curing and gas-generating reactions involving silanol groups can bedepicted as

    .tbd.SiOH+.tbd.SiH→.tbd.Si-O-S-.tbd.+H.sub.2

The curing reaction involving vinyl as the alkenyl radical can bedepicted as .tbd.SiCH=CH₂ +=SiH→SiCH₂ CH₂ Si.tbd., and occurs inconjunction with a reaction between silanol groups, water and/or alcoholpresent in the composition to generate hydrogen.

    YOH+.tbd.SiH+.tbd.SiOY

where Y is .tbd.Si--, R--or H--.

To produce the desired crosslinked polymer structure in the final foameither the organohydrogensiloxane contains at least three silicon-bondedhydrogen atoms or the polyorganosiloxane contains at least 3 silanol orsilicon-bonded alkenyl radicals per molecule.

The silanol- and alkenyl-substituted polyorganosiloxanes are typicallylinear or branched liquid polydiorganosiloxanes that contain two or moresilanol groups or alkenyl radicals per molecule, preferably at least onthe terminal silicon atoms. The alkenyl radical is preferably vinyl orhexenyl, and the silicon-bonded organic groups other than the alkenylradicals are preferably methyl, phenyl, or 3,3,3-trifluoropropyl. Mostpreferably each silicon atom of the polyorganosiloxane contains at leastone methyl radical. These polyorganosiloxanes contain from 0.0002 to 3weight percent of alkenyl radicals and exhibit viscosities of from 1 toabout 500 Pa.s, preferably from 1 to 200 Pa.s.

The organohydrogensiloxanes can have a linear or branched structure andpreferably contain an average of more than two silicon-bonded hydrogenatoms per molecule. Suitable organohydrogensiloxanes contain from 0.5 to2.5 weight percent of silicon-bonded hydrogen and exhibit viscosities offrom 0.01 to about 10 Pa.s.

Preferred compositions for use with the apparatus of the presentinvention contain from 1 to about 10 weight percent of at least onealcohol that is liquid at 25° C. These compositions typically producelow density cured foams and contribute to the resiliency of the finalcured foam. Suitable alcohols include aliphatic and araliphatic alcoholscontaining up to eight carbon atoms. Propanol and benzyl alcohols arepreferred.

In addition to the polyorganosiloxanes containing alkenyl radicalsand/or silanol groups, the organohydrogensiloxane and a curing catalyst,foamable curable organosiloxane compositions may also containingredients typically present in organosiloxane compositions that cureby a hydrosilation reaction. These ingredients include but are notlimited to reinforcing and non-reinforcing fillers, catalyst inhibitorssuch as acetylenic alcohols and cyclic methylvinylsiloxanes, pigments,dyes, heat stabilizers, adhesion promoters and flame retarding agents.

To achieve a useful storage stability at temperatures from 25 to about40° C. organosiloxane compositions that cure by the reaction of anorganohydrogensiloxane with silanol groups and/or alkenyl radicals arepackaged in two parts with the organohydrogensiloxane and the curingcatalyst in separate containers.

The apparatus shown in FIG. 2 of the accompanying drawings is suitablefor use with one-part organosiloxane compositions. The storage stabilityof one-part compositions that cure by a platinum- or tin catalyzedreaction can be increased by encapsulating the catalyst in finelydivided particles of a thermoplastic organic or organosilicon resin.When it is desired to cure the composition, it is heated above thesoftening temperature of the resin. The composition should then bepassed through the mixing zone of the present apparatus to distributethe catalyst uniformly throughout the composition. In this instance theapparatus of FIG. 1 in the accompanying drawings can be modified byreplacing containers 10 and 11 with a single container, conduits 16 and17 with a single conduit, and inserting a heating device downstreamrelative to the mixing zone.

Curable compositions suitable for use with the mixing and dispensingapparatus of the present invention exhibit viscosities of from 1 toabout 200 Pa.s, and can be dispensed at rates from about 10 to about 120grams per minute, depending upon the pressure in the dispensingapparatus and the viscosity of the composition.

In accordance with the present method for preparing cured foams, the twoparts of a curable and foamable organosiloxane composition aretransported under pressure through a mixing manifold which meters andcombines the two streams of ingredients and feeds them into a staticmixer in which the ingredients are blended to homogeneity. As describedin a previous section of this specification, a single storage containerand a heating device are present if a one-part composition containing amicroencapsulated foaming/curing catalyst is used. Two part compositionsare typically maintained at ambient temperature in the apparatus toavoid premature curing of the composition.

From the mixer the composition flows into an exit chamber containing anorifice through which the composition is discharged from the exitchamber into the atmosphere where it foams and cures. The composition isunder pressures in the range of from 200 to 1000 psi from the time itenters the mixing manifold until it emerges from the exit orifice.

The foams produced in accordance with the present method exhibit averagecell diameters of less than 5 mm, preferably less than 1 mm. anddensities in the range from 10 to about 30 pounds per cubic foot.

EXAMPLES

The following examples demonstrate 1) the criticality of the dimensionsof the exit orifice on the cell structure and uniformity of the finalcured foam and 2) how the length to diameter ratio of the static mixercan be reduced to below the minimum value recommended in the prior artfor the type of mixing element used, i.e. a ratio of 29 for the Kenicstype element in the article by Rauwendaal discussed in a precedingsection of this specification.

The apparatus described in the examples represents a preferredembodiment, and should not be interpreted as limiting the scope of theaccompanying claims. Unless otherwise specified all parts andpercentages are by weight and viscosities are the values measured at 25°C.

The two parts of a foamable organosiloxane composition were pumped fromindividual storage containers into the entrance zone of the apparatususing a dual chamber air powered piston pump. The metering device was anair pressure activated valve containing two cylindrical passages, eachwith an area of 38.8 square millimeters.

From the valve the composition entered a mixing manifold that controlledthe relative volumes of the two streams of ingredients entering a 6 cm -long cylindrical passage with an inside diameter of 3.9 mm. This passagewas connected to the input of one of three different types of staticmixers. From the static mixer the composition passed through an exitzone and an exit orifice with a cross-sectional configuration A, B, C,D, E or F.

In B and C, which corresponded to FIG. 3 of the accompanying drawings,and F, which corresponds to FIG. 5, the interior angle (IA) defined bythe conical portion (24) of the wall of the exit zone adjacent to theorifice relative to the cylindrical section of this wall was 150degrees. In D, corresponding to FIG. 3 and E, corresponding to FIG. 4,this angle was 158 degrees.

The diameter of the exit orifice, exit zone and the thickness of thenozzle at the location of the exit orifice of the seven nozzlesevaluated were as follows:

    ______________________________________                                                        Orifice                                                       Nozzle FIG./IA  Thickness Exit Zone  Nozzle                                   Diameter                                                                             (in/mm)  (in/mm)   Diameter (in/mm)                                                                         Thickness                                ______________________________________                                        A      2/90°                                                                           0.030/0.76                                                                              0.345/8.8  0.066/1.7                                B      3/150°                                                                          0.030/0.76                                                                              0.348/8.8  0.129/3.3                                C      3/150°                                                                          0.041/1.04                                                                              0.363/9.2  0.131/3.3                                D      3/158°                                                                          0.030/0.76                                                                              0.386/9.8  0.120/3.0                                E      4/158°                                                                          0.030/0.76                                                                              0.240/6.1  0.120/3.0                                F      5/150°                                                                          0.030/0.76                                                                              0.348/8.8  0.368/9.3                                 G*             0.0830/2.1                                                                              N.A.        0.728/18.5                              ______________________________________                                         *Evaluated for comparative purposes. Nozzle supplied with static mixer wa     used as the exit nozzle. The exit chamber was cylindrical, 0.25 inch in       diameter, tapering to a 0.0830 inch (2.1 mm) diameter nozzle with an          internal angle of 140°. For nozzles A-F the nozzle supplied with       the static mixer was removed.                                            

EXAMPLE 1

This example demonstrates the effect of nozzle configuration anddiameter on the type and diameter of the cells in a low density curedfoam.

Part A of the curable composition used to prepare the low density foamcontained the following ingredients:

63.1 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxaneexhibiting a viscosity of 55 Pa.s; 13.9 parts of a benzene solubleresinous copolymer containing triorganosiloxy units and SiO₂ units inthe molar ratio of about 0.7 mol of triorganosiloxy units per mol ofSiO₂ units, where the triorganosiloxy units are trimethylsiloxy anddimethylvinylsiloxy, and the copolymer contains about 1.8 weight percentof vinyl radicals;

15.1 parts of alumina trihyhdate;

7.32 parts of benzyl alcohol; and

0.54 part of a reaction product of hexachloroplatinic acid andsym-tetramethyldivinyldisiloxane that has been diluted with a liquiddimethylvinylsiloxy terminated polydimethylsiloxane in an amountsufficient to achieve a platinum content of 0.7 weight percent.

Part B of the curable composition contained the following ingredients:

46.2 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxaneexhibiting a viscosity of 55 Pa.s;

10.1 parts of the benzene soluble resinous copolymer described in partA;

26.4 parts of pulverized quartz exhibiting an average particle diameterof 5 microns;

12.6 parts of a 82 weight percent solution in xylene of the reactionproduct of equal parts by weight of (1) a liquidtrimethylsiloxy-terminated polymethylhydrogensiloxane with asilicon-bonded hydrogen content of about 1.6 weight percent, and (2) aresinous organosiloxane copolymer consisting essentially of (CH₃)₃ SiO₂and SiO₂ unit with a molar ratio of CH₃)₃ SiO_(1/2) SiO₂ units of from0.4:1 and 1.2:1, and from about 0.5 to about 3 weight percent ofhydroxyl groups; and

4.7 parts of a trimethylsiloxy-terminated polydiorganosiloxane having anaverage of five methylhydrogensiloxane units and three dimethylsiloxaneunits per molecule with a silicon-bonded hydrogen atom content in therange from about 0.7 to 0.8 weight percent.

The viscosity of an uncured mixture of parts A and B was between 60 and70 Pa.s.

The static mixer used as the mixing zone was 8.75 inches (22.2 cm.)long, 0.25 inch (0.64 cm.) in internal diameter and contained 32 Kenicstype elements.

The air pressure supplied to the pump was 50, 60, or 75 psig (0.34, 0.41or 0.52 MPa.) and the pump had a power factor of 12. To ensurereproducibility of the samples, all were obtained during the upstroke ofthe pump cycle.

The samples were from 25 to 75 grams in weight and were collected on aflat surface located about 1 cm. below the exit orifice. The sampleswere allowed to remain under ambient conditions until they cured, whichtypically required from 1/2 to 4 hours. The time required to develop anon-tacky surface was about 7 minutes.

Samples measuring 1.5 by 1.5 inches (3.8 by 3.8 cm.) were cut from eachof the cured foams for evaluation. Evaluation included an examination ofthe surface of each sample, the cells in the area immediately beneaththe surface, and in the remainder of the sample. In addition, the sizerange of the cells were measured. In many samples the cell size in thearea immediately below the surface was different than the size in theremainder of the foam.

The density of the foam samples were about 12 pounds per cubic foot.

The results of the evaluation of the foam samples are recorded inTable 1. For comparative purposes foams were prepared without using anozzle of the present invention. In this instance the foamablecomposition was collected using the nozzle supplied as part of thestatic mixer. The diameter of the exit orifice of this nozzle was 0.0830inch (2.1 mm). This nozzle was removed and replaced by one of thenozzles identified as A, B, C, D, E, and F to prepare the other foamsamples listed in Table 1.

                                      TABLE 1                                     __________________________________________________________________________            Pump                                                                  Sample  Pressure                                                                           Cell Structure                                                   No. Nozzle                                                                            (psig)                                                                             Surface    Sub-Surface  Remainder                                __________________________________________________________________________     1* None                                                                              75   open, >5 mm                                                                              open, 3-5 mm same                                      2* None                                                                              60   open & closed, >5 m                                                                      oval, open, 3-5 mm                                                                         same                                      3  E   60   closed, ≦1 mm                                                                     oval, closed, ≦1 × 2                                                          same                                      4  B   75   open, ≦1 mm                                                                       closed, ≦1 mm                                                                       open, 1 × 5 mm.                     5  B   60   open, ≦1 mm                                                                       ≦1 mm, depth = 3 mm                                                                 oval, 1-5 mm                              6  B   50   open, ≦1 mm                                                                       ≦1 mm, depth = 10 mm                                                                oval, 1 × 4 mm                      7  C   75   open, ≧1 mm                                                                       oval, ≦3 × 7 mm                                                               same                                      8  C   60   open, 1 mm 1-2 mm, depth =0 15 mm                                                                     2 × 5 mm**                          9  C   50   closed, ≦1 mm                                                                     ≦1 mm throughout                                                                    about 5% < 1                             mm                                                                            10  F   75   open, ≧2 mm                                                                       ˜2 mm, depth = 20 mm                                                                 oval, <2 × 6 mm                    11  F   60   closed, ≦2 mm                                                                     1-2 mm, uniform                                                                            same                                     12  F   50   closed, ≦2 mm                                                                     ≦1 mm, depth = 10 mm                                                                oval, ≦3 mm                       13  A   75   closed, ≦2 mm                                                                     1-2 mm, depth = 2 mm                                                                       oval, ˜2 × 4 mm              14  A   60   open + closed, 2 mm                                                                      1-3 mm, non-uniform                                                                        same                                     15  A   50   closed, 1-3 mm                                                                           1-3 mm, uniform                                                                            same                                     16  D   75   closed, 1-3 mm                                                                           ≦1 mm 80% = ≦1 mm                       17  D   50   closed, 1-2 mm                                                                           ≦1 mm, more uniform than No.                   __________________________________________________________________________                            16                                                     *Comparative Example, used nozzle supplied as part of static mixer            **Non-uniform size distribution                                          

EXAMPLE 2

This example demonstrates the effect of exit zone configuration, nozzlesize and the number of static mixer elements on the size and uniformityof cells in a high density foam exhibiting a density of about 10 poundsper cubic foot.

Part A of the curable composition used to prepare the foam contained thefollowing ingredients:

39.85 parts of a dimethylvinylsiloxy terminated polydimethylsiloxanehaving a viscosity of about 55 Pa.s;

32.68 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxaneexhibiting a viscosity of about 9 Pa.s at 25 degrees C.

7.17 parts of a benzene soluble resinous copolymer containingtriorganosiloxy units and SiO₂ units in the molar ratio of about 0.7 molof triorganosiloxy units per mol of SiO₂ units, where thetriorganosiloxy units are trimethylsiloxy and dimethylvinylsiloxy, andthe copolymer contains about 1.8 weight percent of vinyl radicals;

13.24 parts of calcium carbonate

3.82 parts of 1,4-butanediol;

1.33 part of a reaction product of hexachloroplatinic acid andsym-tetramethyldivinyldisiloxane that has been diluted with a liquiddimethylvinylsiloxy terminated polydimethylsiloxane in an amountsufficient to achieve a platinum content of 0.7 weight percent; and

0.19 part of cyclic methylvinylsiloxanes.

Part B of the curable composition contained the following ingredients:

58.9 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxaneexhibiting a viscosity of 55 Pa.s;

13.8 parts of the benzene soluble resinous copolymer described in partA;

14.6 parts of an 82 weight percent solution in xylene of a reactionproduct of equal weights of (1) a liquid trimethylsiloxy-terminatedpolymethylhydrogensiloxane with a silicon-bonded hydrogen content ofabout 1.6 weight percent, and (2) a resinous organosiloxane copolymerconsisting essentially of (CH₃)₃ SiO_(1/2) and SiO₂ units with a molarratio of CH₃)₃ SiO_(1/2) SiO₂ units of from 0.4:1 and 1.2:1; thecopolymer can be prepared as described in U.S. Pat. No. 2,676,182, andtypically contains from about 0.5 to about 3 weight percent of hydroxylgroups;

9.1 parts of a liquid trimethylsiloxy-terminatedpolymethylhydrogensiloxane with a silicon-bonded hydrogen content ofabout 1.6 weight percent; and

3.6 parts of a trimethylsiloxy-terminated polydiorganosiloxane having anaverage of five methylhydrogensiloxane units and three dimethylsiloxaneunits per molecule with a silicon-bonded hydrogen atom content in therange from about 0.7 to 0.8 weight percent.

12.6 parts of a 82 weight percent solution in xylene of the reactionproduct of equal parts by weight of (1) a liquidtrimethylsiloxy-terminated polymethylhydrogensiloxane with asilicon-bonded hydrogen content of about 1.6 weight percent, and (2) aresinous organosiloxane copolymer consisting essentially of (CH₃)₃SiO_(1/2) and SiO₂ unit with a molar ratio of CH₃)₃ SiO_(1/2) SiO₂ unitsof from 0.4:1 and 1.2:1, and from about 0.5 to about 3 weight percent ofhydroxyl groups; and

4.7 parts of a trimethylsiloxy-terminated polydiorganosiloxane having anaverage of five methylhydrogensiloxane units and three dimethylsiloxaneunits per molecule with a silicon-bonded hydrogen atom content in therange from about 0.7 to 0.8 weight percent.

The viscosity of an uncured mixture of parts A and B was between 20 and25 Pa.s.

Foam sample were prepared and evaluated as described in Example 1. Thenozzles used were types B and E described in Example 1. For comparativepurposes foams were prepared using the nozzle supplied with the staticmixer.

In all instances the diameter of the static mixer was 0.25 inch (6.35mm). The mixer referred to as I was 8.75 inches (22.2 cm.) long andcontained 32 Kenics type elements (L/D ratio=35) ; the mixer referred toas II was 2.75 inches (6.98 cm.)long and contained 8 Kenics typeelements (L/D ratio=11) and the mixer referred to as III was 4.75 inches(12.07 cm) long and contained 16 Kenics type elements (L/D ratio=19).

The air pressure supplied to the pump was 50, 60, or 75 psig (0.34, 0.41or 0.52 MPa.) and the pump had a power factor (output pressure/inputpressure) of 12. To ensure reproducibility of the samples, all wereobtained during the upstroke of the pump cycle.

All of the samples were from 25 to 75 grams in weight and were collectedon a flat surface located about 1 cm. below the exit orifice. Thesamples were allowed to remain under ambient conditions until theycured, which typically required from 1/2 to 4 hours. The time requiredto develop a non-tacky surface was about 7 minutes.

Samples were prepared and evaluated as described in the precedingExample 1. The density of the foam samples were about 10 pounds percubic foot.

The results of the evaluation of the foam samples are recorded in Table2. For comparative purposes foams were prepared without using a nozzleof the present invention. In this instance the foamable composition wascollected using the nozzle supplied as part of the static mixer. Theorifice diameter of this nozzle 0.0830 inch (2.1 mm). This nozzle wasremoved and replaced with nozzle type B or E to prepare the other foamsamples listed in Table 2.

                                      TABLE 2                                     __________________________________________________________________________            Pump                                                                  Nozzle                                                                            Mixer                                                                             Pressure                                                                           Cell Structure                                                   Type                                                                              Type                                                                              (psig)                                                                             Surface   Sub-Surface       Remainder                            __________________________________________________________________________    None*                                                                             I   75   rough, open cells                                                                       1-2 mm, depth = 15 m                                                                            large gaps                           None*                                                                             I   60   rough, open cells                                                                       1-5 mm, non-uniform                                    None*                                                                             I   50   less rough than 1                                                                       oval, uniform, 3-5 mm                                  None*                                                                             I   25   sm. amt. open cells                                                                     1-5 mm, most uniform                                   E   I   75   50% open cells                                                                          1-5 mm, large cavities                                 E   I   60   ˜40% open cells                                                                   Oval, 3-10 m, 80% < 5 mm                               E   I   50   ˜10% open cells                                                                   <1 mm, depth = 2 m                                                                              1-5 mm                               B   I   75   no open cells                                                                           ≦1 mm throughout, 90% uniformity                B   I   60   no open cells                                                                           ≦1 mm, depth = 10 mm                                                                     oval, 1-2                            mm                                                                            B   I   50   similar to sample 9                                              B   II  70   10% open cell                                                                           <1-2 mm, depth = 5 mm                                                                           oval, 2-5 m                          B   II  30   open cells                                                                              burst cell walls, 1- 5 mm, stiff foam                  B   III 70   --        <1 mm throughout foam                                  B   III 30   smooth, no cells                                                                        <1 mm, depth = 5 mm                                                                             ≦1 mm                         __________________________________________________________________________     *Comparative example, used nozzle supplied with static mixer             

EXAMPLE 3

This comparative example demonstrates the need for a nozzle of theconfiguration associated with the present apparatus for preparing highdensity foams at high production rates.

Part A of the foamable composition was prepared by blending thefollowing ingredients to homogeneity:

63.1 parts of the polydimethylsiloxane described in Example 2; 13.9parts of the resinous organosiloxane copolymer described in Example 2;

15.1 parts of alumina trihydrate

7.3 parts of benzyl alcohol; and

0.5 part of a reaction product of hexachloroplatinic acid andsym-tetramethyldivinyldisiloxane that had been diluted with a liquiddimethylvinylsiloxy terminated polydimethylsiloxane in an amountsufficient to achieve a platinum content of 0.7 weight percent.

The two parts of the foamable composition were placed in the two storagecontainers of the mixing and dispensing apparatus used to prepare thefoam samples of Example 1. In this instance the nozzle was the onesupplied with the static mixer. The diameter of the exit orifice of thisnozzle was 0.095 inch (2.4 mm.). The mixer was 7.87 inches (20 cm.)long, 0.37 inch (0.94 cm) in diameter and contained 24 Kenics typeelements. Part B of the foamable composition was prepared by blendingthe following ingredients to homogeneity:

46.2 parts of the polydimethylsiloxane of Example 2;

10.1 parts of the resinous organosiloxane copolymer described in Example2;

12.6 parts of a 82 weight percent solution in xylene of the reactionproduct of equal parts by weight of (1) a liquidtrimethylsiloxy-terminated polymethylhydrogensiloxane with asilicon-bonded hydrogen content of about 1.6 weight percent, and (2) aresinous organosiloxane copolymer consisting essentially of (CH₃)₃SiO_(1/2) and SiO₂ unit with a molar ratio of CH₃)₃ SiO_(1/2) :SiO₂units of from 0.4:1 and 1.2:1, and from about 0.5 to about 3 weightpercent of hydroxyl groups; and

4.7 parts of a trimethylsiloxy-terminated polydiorganosiloxane having anaverage of five methylhydrogensiloxane units and three dimethylsiloxaneunits per molecule with a silicon-bonded hydrogen atom content in therange from about 0.7 to 0.8 weight percent

The pump pressure was 60 psig and the flow rate of the curablecomposition was varied by adjusting the size of the channel in theair-actuated valve (metering device). The flow rates used were 25, 100and 120 grams per minute.

The quality of the resultant cured foam was evaluated as described inExample 1, and the results are recorded in the following table 3.

                                      TABLE 3                                     __________________________________________________________________________    Flow rate                                                                           Cell Structure                                                          (g/min)                                                                             Surface       Sub-Surface Remainder                                     __________________________________________________________________________     25   Closed cells, small bubbles                                                                 ≦2 mm, depth = 1 cm                                                                1-2 mm, oval                                  100   Textured, large bubbles                                                                     >3 mm, voids                                              120   Textured, large bubbles                                                                     >3 mm, voids                                              __________________________________________________________________________

This example demonstrates that while prior art nozzle configurations canbe used to prepare high density foams, the flow rate must be below 100grams per minute.

That which is claimed is
 1. A method for blending and dispensing afoamable organosiloxane composition comprising anorganohydrogensiloxane, a reactant selected from the group consisting ofcurable polyorganosiloxanes containing silanol groups, water and liquidalcohols, and a curing catalyst, the method comprising transporting saidcomposition under pressure first through a mixing zone consistingessentially of a channel having an inlet and an outlet and containing aplurality of static mixing elements positioned within the channel, wherethe ratio of the length of said channel to its diameter is at least 11,and second through an exit zone communicating with the outlet of saidchannel and comprising a nozzle containing an exit orifice where thediameter of said exit orifice does not exceed 1.50 mm.
 2. A methodaccording to claim 1 where said composition is transported through saidmixing and exit zones under a pressure of from 200 to 1000 psi (1.4 to 7MPa), the flow rate of said composition through said apparatus is from10 to 120 grams per minute, and the foam exhibits an average celldiameter of less than 5 mm and a density of from 10 to 30 pounds percubic foot (160 to 480 kg. cm³).
 3. A method according to claim 2 wheresaid composition comprises an organohydrogensiloxane, at least onecurable polyorganosiloxane containing at least two groups bonded tosilicon selected from the group consisting of hydroxyl groups andalkenyl radicals, and an amount of a curing catalyst sufficient topromote foaming and curing of said composition, with the proviso that ifthe composition does not contain an amount of a hydroxyl-containingpolyorganosiloxane sufficient to react with said organohydrogensiloxaneto generate the gaseous hydrogen required to form a foam, saidcomposition contains an amount of water or an alcohol sufficient to formsaid foam, where the silicon-bonded organic groups present in saidpolyorganosiloxane and said organohydrogensiloxane are selected from thegroup consisting of unsubstituted and substituted monovalent hydrocarbonradicals.
 4. A method according to claim 3 where at least one of thehydrocarbon radicals bonded to each silicon atom of saidpolyorganosiloxane and said organohydrogensiloxane is methyl and theremainder are selected form the group consisting of methyl, phenyl and3,3,3-trifluoropropyl, said alkenyl radical is vinyl, said curingcatalyst is a tin compound, a platinum group metal or a compound of saidmetal, the viscosity of said composition is from 1 to 200 Pa.s, and saidcomposition comprises an alkenyl-containing polyorganosiloxane and from1 to 10 weight percent, based on the weight of said composition, of analcohol.
 5. A method according to claim 4 where said compositioncontains a reinforcing or non-reinforcing filler.